The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
In computer systems that use 32-bit bytes or words for instructions, data, or data transfers, the term “octet” refers to eight-bit portions of the bytes or words. Border Gateway Protocol version 4 (BGP4 or BGP), defined in Internet Engineering Task Force (IETF) Request for Comments (RFC) 1771, is the inter-domain routing protocol used to interconnect autonomous systems in both the public Internet and virtually all private internetworks. Currently, BGP messages uniquely identify an autonomous system (AS) using numeric values that are two octets in length. This limits the range of available AS numbers to between 1 and 216, or 65,536. As a result, the public Internet is quickly running out of AS numbers to assign to newly connecting networks.
In response, several members of the IETF have proposed modifying BGP for use with a 4-octet or byte-length AS number. Converting router BGP software to use 4-octet AS numbers is attractive because the number of unique autonomous systems that can be represented in BGP messages increases to 232.
Pertinent literature in the field includes: Chen, E. and Q. Vohra, “BGP support for four-octet AS number space”, RFC draft-ietf-idr-as4bytes-10.txt, July 2004 (referred to herein as “[BGP-4BYTES]”); Chen, E. and S. Sangli, “Dynamic Capability for BGP-4”, RFC draft-ietf-idr-dynamic-cap-07.txt, July 2004 [BGP-CAPABILITY]; Sangli, S., Tappan, D., and Y. Rekhter, “BGP Extended Communities Attribute”, RFC draft-ietf-idr-bgp-ext-communities-09.txt, July 2005 [BGP-EXTCOMM].
However, no proposal provides an acceptable approach to transition from the existing 2-octet AS number space to a new 4-octet AS number space. In one proposed approach, 4-octet AS numbers are used in routers within a particular AS, but only 2-octet numbers are used in communications with other nodes until all routers in the public Internet are upgraded to support 4-octet AS numbers. This appears to be an untenable solution, because the Internet probably will run out of available unique 2-octet AS numbers long before all routers in the Internet can be upgraded.
Based on the foregoing, there is a clear need for an improved approach for transitioning from 4-octet AS numbers to 2-octet AS numbers.